Sand pack-aided formation sand consolidation

ABSTRACT

In treating a cased and perforated well to prevent sand inflow, a resin solution from which self-curing epoxy resin is subsequently precipitated is injected into the reservoir and the perforated interval of the casing is filled with grains suspended in and permeated with the resin solution. The resin is allowed to precipitate and cure in the casing and reservoir and at l east a portion of the consolidated mass of grains that is formed within the casing is drilled-out.

United States Patent [1 1 Pramann 1 51 Jan. 9, 1973 [54] SAND PACK-AIDEDFORMATION SAND CONSOLIDATION [75] Inventor: James A. Pramann, Metairie,La.

[73] Assignee: Shell Oil Company, New York, N.Y.

3,294,166 12/1966 Havenaar et al. ..l66/295 3,327,783 6/1967 Ayers,..166/276 X 3,404,735 10/1968 Young et al. 1 66/295 3,476,189 11/1969Bezemer et al..... ....166/295 3,548,942 12/1970 Terry 1 66/2763,621,915 10/1969 Bruist et a1. 166/276 Primary Examiner-Stephen J.Novosad Attorney-H. W. Coryell and Harold L. Denkler [57] ABSTRACT Intreating a cased and perforated well to prevent sand inflow, a resinsolution from which self-curing epoxy resin is subsequently precipitatedis injected into the reservoir and the perforated interval of the casingis filled with grains suspended in and permeated with the resinsolution. The resin is allowed to precipitate and cure in the casing andreservoir and at 1 east a portion of the consolidated mass of grainsthat is formed within the casing is drilled-out.

5 Claims, 2 Drawing Figures PATENTEUJAK 9 ma 3709.298

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J. A Pra mann INVENTOR sANo PACK-AIDED FORMATION sANn CONSOLIDATIONBACKGROUND OF THE INVENTION This invention is a.well treatment forpreventing an inflow of sand. it is particularly suitable for use inwells that have been cased and perforated within reservoirs which are,or may become, unconsolidated.

In respect to sand inflow or packing sand or gravel the terms refer tosolid particles that have a sand or gravel size range and are'composedof glass beads, silica, quartz, walnut shells, portions of reservoirformation grains and/or cementing materials, or substantially any solidparticles that may be used to restrain the inflow of formation grains ormay comprise the grains of an unconsolidated reservoir formation.

Previously proposed sand controlling treatments for cased and perforatedwells have included procedures such as:

Coating packing grains with a self-curing epoxy resin material,suspending the coated grains in a compatible liquid having only alimited miscibility with the resin solvent, and pumping the suspensioninto the well to pack the coated grains in the perforation tunnels andassociated voids within the reservoir (or, if desired, to pack themaround a screen or liner within the borehole) to form aresin-consolidated mass, as described in a copending patent applicationby E. H. Bruist, T. W. Hamby, T. A. Simon and R. N. Tuttle, Ser. No.867,631, tiled Oct. 20, 1969 now U.S. Pat. No. 3,621,915;

Pumping in a slurry of resin-coated. grains, such as those describedabove, through a well a conduit having a discharge opening that israised from near the lowermost to near the uppermost perforation whileusing flow rates and rates of raising the discharge opening such that afluidized bed of coated grains is formed near each perforation, asdescribed in a copending patent application by T. A. Simon and R. S.Torrest, Ser. No. 82,925, filed Oct. 20, 1970;

Pumping in a slurry of resin-coated grains, such as those describedabove, in an amount that is correlated with the volume of the perforatedinterval 'of casing and associated voids within the reservoir in orderto form a i pack of the coated grains within the casing and the voidsthat extends from below to above the perforated interval, andsubsequently drilling-out the resin-consolidated mass of grain that isformed within the casing, as described in a copending patent applicationby J. M. Waid, Ser. No. 121,191 filed Feb.3, 1971;

injecting a substantially solids-free resin solution from which aself-curing epoxy resin material is subsequently precipitated into thereservoir and-maintaining it substantially static to allow the resin tobe precipitated and the reservoir formation to be consolidated in situ,as described in U.S. Pat. No. 3,294,166 by l. Havenaar and F. H. Meys;and

Pumping into the well a substantially solids-free resin solution fromwhich a self-curing epoxy'resin material is subsequently precipitated,substantially asdescribed above, in a volume and manner such that theresin solution permeates the near well portion of the reservoir andfills the casing from below to above the perforated interval,maintaining the solution substantially static until the resinprecipitates and cures, and removing any resin coated granular materialsthat might impede the passage of tolls or equipment within the casing,as

forations open into reservoir portions of higher or lower permeabilitiesand some are temporarily plugged by debris (such as that from theperforating materials or equipment or the well casing or cement) or thelike. A well treatment in which a suspension of resin-coated grains isflowed through the perforations tends to form a resin-consolidated sandpack in and around only the most permeable perforations while providinglittle or no protection against slumping or collapsing within theunconsolidated reservoir formation around a plugged or low permeabilityperforation. This may allow a subsequent casing deformation anddestruction of the consolidated granular masses that were formed nearthe open perforations. A well treatment in which a substantiallysolid-free resin solution is injected into the pores of the reservoirformation tends to consolidate the formation near the mostopenperforations while providing little or no consolidation around pluggedperforations leaving voids within the reservoir. This may allow asubsequent reservoir slumping and casing deformation accompaniedbyadestruction of the grain interbonding in the consolidated portions ofthe reservoir, If such an injection of resin solution is preceded by asand and/or gravel packing treatment, the packing grains tend to bedeposited in the voids around the open perforations, but thesubsequently injected sand consolidating fluid tends to redistribute thepacking grains and reopen the voids. In addition, if a mass or column ofsand or gravel is deposited in the well before the resin solution .isinjected, most of the resin solution tends to enter the upperperforations, via flow paths involving theleast travel through the sandor gravel.

SUMMARY OF THE INVENTION In accordance with this invention a sandcontrolling treatment of a cased and perforated well ina reservoir thatis (or is apt to become) unconsolidated is improved by permeating theadjacent portions of the reservoir with a resin solution thatsubsequently precipitates a self-curing epoxy resin, filling theinterior of the perforated portion of the casing and associatedperforation tunnels'and voids within the reservoir with a mass ofpacking grains that is permeated with the resin solution, allowing theresin solution to remain static while the resin precipitate s and cures,and, subsequently, drilling out a portion of the consolidated mass ofgrains that is formed within the casing.

This invention is at least in part premised on the discovery that such aresin solution can be displaced through a well conduit ahead of aportion of resin solution containing suspended packing grains anddisposed within the well and the surrounding portion of the reservoir sothat the resin solution-permeated grains are packed into the formationvoids, perforation tunnels, and perforated intervalof casing adjacent tothe solids-free resin solution that has been injected into the reservoirwithout causing an economically unfeasible'amount of the resin solutionto be-injected.

Resin solutions can be utilized as carrier fluids for the packing grainsat pumping rates that can be attained without fracturing the reservoirsbeing treated. The subsequent precipitation and curing of the resinousmaterial forms a substantially continuous resin-consolidated mass ofinjected grains and reservoir formation grains that extends from withinthe perforated interval of casing to within the surrounding portion ofthe reservoir. The drilling out of a portion of the consolidated mass ofgrains within the casing always leaves at least a portion of such aconsolidated mass of grains that extends from within the reservoir andthrough the perforation tunnels to the inner diameter of the casing.

In a preferred embodiment of the invention, the injection of packinggrain-carrying resin solution is preceded by the running in of acentered drillable structure that extends along the perforated intervalof the casing and is substantially hollow, or has a low resistance tobeing drilled along its center, and is arranged to contain and guide apilot portion of a bit or mill for drilling out such materials. Thedrilling out of only a central non-gauge portion of the mass resinconsolidated grains that extends from within the reservoir to within thecasing (by guiding a non-gauge drilling means along the central portionof the drillable structure within the perforated interval) ensures aneffective sand control even though neither the resin solution nor resinsolution-suspended packing grains have entered into all of theperforations.

' DESCRIPTION or THE DRAWING FIG. 1 is a schematic partiallycross-sectional view'of a well being treated in accordance with thisinvention.

FIG. 2 is a similar illustration of anenlarged portion of the materialsshown in FIG. 1.

DESCRIPTION OF THE INVENTION l and resin solution 16 have been injectedinto the reservoir formation 8 around the perforated interval of casing.The perforated interval-of casing and associated perforation tunnels andvoids within the reservoir formation have been packed with packingmaterial grains 15 to form a mass of contiguous grains which ispermeated by the resin solution 16. The resin solution extends above themass to an interface 18 between the resin solution 16 and a spacer fluid14 which was displaced through tubing 12 ahead of a displacement fluid17. At the stage shown in FIG. 1, the fluids are being kept stationerywhile resinous material is being precipitated from resin solution 16 andcured to interconnect the packing material grains l5 and the grains ofthe reservoir formation 8 into an integral permeable mass a (FIG. 2) ofresin-consolidated grains.

In FIG. 2 a portion of the consolidated mass of grains and thecentralized drillable, structure 6 have been drilled out to leave acentral portion ofthe interior of casing 3 filled with drilling fluid l9and an annular ring of the mass of consolidated grains 15a.

The above materials and the procedures for their in stallation or usewithin a well can involve materials and techniques known to thoseskilled in the art.

The pretreatment fluids and resin solutions are.

preferably materials of the types described in U.S. Pat; No. 3,294,166and 3,476,189. Such resin solutions deposit self-curing epoxy resinmaterials in the grainto-grain contacts between a mass of contiguousgrains, by means of phase separation and capillarity. To enhance thisaction the grains and/or reservoir sand should be oil-wet. The injectionof the resin solution is preferably preceded by three pre-flushes. Thefirst is preferably a light oil, such as diesel oil, that displacesresidual crude oil, substantially fills the pores, and reduces the watersaturation to a residual water saturation. The next is an oil and watermiscible material,

such as isopropyl alcohol, which displaces both the previously injectedoil and the residual water. The mutually miscible solvent is thendisplaced with the medium range oil that tends to leavethe formationoil-wet and to displace the mutually miscible solvent so that it willnot come intocontact with the resin solution and accelerate the curingof the resin. The injected resin solution preferably contains about 18per cent resin forming components and about 82 percent solvent. When thepartially polymerized resinous materialsare precipitated, they are thewetting phase and cap'illarity draws these materials into thegrain-to-grain contacts where the resinous materials'are held until theyharden. In general, the result is a consolidated mass in which thecentralportion of the pore spaces between the grains is filled withsolvent.

The packing grains can be substantially any type of hard particleshaving a size such that they forma sand pack which is permeable to aninflow of fluid but impermeable to substantially all of the formationgrains. The exclusion of the formation grains is important and ispreferably accomplished by using relatively wellrounded packing grainsthat have a generally spherical shape and a relatively narrow range ofgrain sizes with a median grain size which is not more than about 7times larger than the median size of the grains in the reservoirformation.

In the present process, the packing grain size is preferably correlatedwith the formation grain size, as described above, to provide a packthat excludes substantially all particles of the reservoir grain sand.This correlation is distinctively different from a procedure, such asthat described in US. Pat. No. 3,548,942, in which a bed of relativelycoarse particulate material is deposited in the well bore adjacentto'the formation prior to injecting the solutions employed for sandconsolidation purposes. Such beds through which the resin solutions areinjected are used to provide large surface areas on which films ofpre-polymerized resincanbe accumulated without plugging the porespacesthrough 'which the sand consolidating material solutions mustresin solution that enter differently located perforations. In addition,in the present process, the beds of grains are uniformly permeated witha solution of selfcuring resin forming ingredients and are uniformlybonded together by the uniform deposition and curing of suchingredients.

in the suspending of packing grains in the resin solution and injectingthe suspension into the well in accordance with the present process, theinitial portions of resin solution can contain little or no suspendedsand. However, particularly in a remedial operation in a well from whicha significant amount of formation sand has been entrained in fluidsflowing into the well to leave one or more voids within the reservoir, asigniflcant amount of packing sand may be desirable to pack each void.

in the present process, resin solution is commonly formulated andinjected in units of 100 gallons per foot of perforated interval and therates of pumping are to some extent controlled by the injection pressurethat can safely be applied without fracturing the reservoir. In numerousunconsolidated reservoirs one unit of resin solution permeates a zonearound the well having a radius in the order of 3 feet. Where asignificant amount of sand is needed to pack relatively large voids,sand is preferably suspended in the initial portion of the suspensionbut then are preferably kept relatively dilute, with the concentrationsincreasing with time until the later injected portions are relativelyconcentrated. When the last portions of resin solutionsuspended grainshave been displaced through a well conduit to near the perforated zone,the fluid flow rate is reduced to cause a sand-out" or deposition of theentrained sand.

EXAMPLE I WELL TESTS The well to be treated was completed with aperforated 5% inch casing in a 5 foot sand interval in which an initialin situ sand consolidation, with an injected resin solution from which aself-curing epoxy resinous material was subsequently precipitated, hadfailed. Ten units of a resin solution of the preferred type describedabove were used with sacks (100 pound sacks) of 0.017 inch by 0.033 inchgravel being blended in the last five units with a continuousproportioner. The initial portions of the resin solution were injectedat a rate of about 1 bpm (barrels per minute) and a sand-out wasachieved, when the latter portions were near the perforated interval.The sand-out was achieved by reducing the pump rate to about onefourthbpm (i.e., in response to an injection pressure of 3,000 psi). The resinsolution was maintained substantially static to allow resin material tobe precipitated and cured. The top of the gravel was found to be about67 feet above the top of the perforations. The gravel was drilled out ata rate of 2% feet per minute with 5,000 pounds weight on the bit of aconventional drill string assembly. ln tests conducted after thetreatment, the well was flowing 176 barrels per day of oil with 19 percent water (5,682 gas-oil ratio and 1,350 psi tubing pressure) with atrace of sand.

The present process can be used in conjunction with a fluidized bedslurry injection procedure such as that described and claimed in theSer. No. 82,925, filed Oct. 20, 1970 copending patent applicationreferred to above. In such a procedure, an injection tubing string, suchas tubing 12, is extended into the well bore to near the bottom of theinterval to be packed and the slurry of the packing materials in theresin solution is pumped through the tubing string while the string isbeing raised at a rate correlated with the pumping rate to maintain afluidized bed of packing material around the end of the tubing string asit moves through the interval to be packed.

What is claimed is:

l. in a sand control treatment in which a resin solution from whichself-curing epoxy-resin material is subsequently precipitated is pumpedthrough a well conduit in a cased and perforated well and is injectedinto the adjacent reservoir formation, the improvement comprising:

suspending grains in at least a portion of the resin solution, with saidgrains having a size adapted to form a pack that prevents an inflow ofreservoir formation grains;

pumping the resin solution and suspended grains through the well conduitso that a portion of the reservoir formation is permeated by the resinsolution and the suspended grains are packed into a resinsolution-permeated mass of grains that extends as a substantiallycontinuous mass of contiguous grains from below to above the perforatedsection within the casing, extends through the perforations in thecasing wall, extends into and fills voids within the adjacent reservoirformation, and extends into contact with the adjacent portions of thereservoir formation;

maintaining the resin solution substantially static within the well andthe reservoir until the resin material has precipitated and cured; and

drilling out at least a portion of the resultant resinconsolidated massof grains that is formed within the casing. j

2. The process of claim 1 in which: 7

a drillable structure adapted to guide a drilling means is centeredwithin the casing along the perforated interval prior to the pumping inof the suspended Y grains; and

a non-gauge portion of the consolidated mass of grains within the casingis drilled out by guiding a drilling means along said drillablestructure.

3. The process of claim 1 in which the median size of said packinggrains is not more than about 7 times that of the reservoir formationgrains.

4. The process of claim 1 in which the grain suspending slurry isinjected through a tubing string havinga discharge location that israised from near the bottom to near the top of the perforated intervalat rates correlated with the injection rate to form a fluidized bed ofparticles in and around each of the perforations.

5. A well treatment which comprises:

injecting resin solution from which self-curing epoxy resin material issubsequently precipitated through the-perforation tunnels of aperforated section of well casing and into an adjacent substantiallygranular reservoir formation;

suspending in said resin solution grains having a size adapted to form apack which excludes the entry of any sand grains from the reservoirformation;

pumping said suspension into said perforated section of easing so thatthe suspended grains are deposited to form a substantially continuousmass' of contiguous grains extending from within the casing andthroughout the perforated interval to

2. The process of claim 1 in which: a drillable structure adapted toguide a drilling means is centered within the casing along theperforated interval prior to the pumping in of the suspended grains; anda non-gauge portion of the consolidated mass of grains within the casingis drilled out by guiding a drilling means along said drillablestructure.
 3. The process of claim 1 in which the median size of saidpacking grains is not more than about 7 times that of the reservoirformation grains.
 4. The process of claim 1 in which the grainsuspending slurry is injected through a tubing string having a dischargelocation that is raised from near the bottom to near the top of theperforated interval at rates correlated with the injection rate to forma fluidized bed of particles in and around each of the perforations. 5.A well treatment which comprises: injecting resin solution from whichself-curing epoxy resin material is subsequently precipitated throughthe perforation tunnels of a perforated section of well casing and intoan adjacent substantially granular reservoir formation; suspending insaid resin solution grains having a size adapted to form a pack whichexcludes the entry of any sand grains from the reservoir formation;pumping said suspension into said perforated section of casing so thatthe suspended grains are deposited to form a substantially continuousmass of contiguous grains extending from within the casing andthroughout the perforated interval to within the adjacent reservoirformation; correlating the volume and disposition of said resin solutionso that it extends as a continuous body of grain-permeating fluidthroughout said substantially continuous mass of sand and an adjacentportion of said reservoir formation; maintaining said resin solutionsubstantially static to cause said resin material to precipitate andcure; and drilling out at least a portion of the resultantresin-consolidated mass of grains that is formed within the casing.